An Algorithm for the Interpretation of Cardiopulmonary Exercise Tests

clinical investigations An Algorithm for the Interpretation Cardiopulmonary Exercise Tests*

of

William L. Eschenbacher, M.D., EC.C.P.; and Anthony .\lannina, M.D.

We have developed and are using an algorithm for the interpretation of cardiopulmonary exercise tests that are performed in our Pulmonary Diagnostic Service Department. As its decision points, this algorithm uses routinely obtained measurements from the results of these exercise tests, such as Vo., Vco,, VJo:, SaO,, HR, and AT. Using the algorithm results in an objective determination of limitation to exercise and allows for the differentiation between pulmonary and cardiac or circulatory limitation. This

testing has been used by cardiologists and E xercise pulmonologists for the evaluation of the heart and lungs under the physiologic stress of increasing external workloads. Cardiac stress tests were developed to evaluate possible ischemic changes that may occur as the pressure-pulse product or the modified tension time index is increased. 1 During a cardiac stress test, changes in the ECG and blood pressure are monitored during increasing workloads. Cardiopulmonary exercise tests in addition can help determine other potential limiting factors to exercise: the lungs; or the heart; or both. Thus, in addition to monitoring the ECG and blood pressure, cardiopulmonary exercise tests monitor exhaled oxygen, carbon For editorial comment see page 257 dioxide, VE, and arterial blood gas tensions or oxygen saturation (or both). Although much has been written regarding the basic physiologic responses to exercise, little information has been provided for a routine and consistent approach to the interpretation of a cardiopulmonary exercise test. One example of an interpretative technique is shown in a recent book by \Vasserman and others. 2 We have developed and are currently using a simple algorithm for the interpretation of cardiopulmonary exercise tests. This algorithm is based upon the routinely obtained parameters of \:E, Vo2 , Vco 2 , *From the Pulmonar,· and Critical Care 1\ledidne Dh·ision, llniversity of Mk·higan f.tedkal Cenlt•r, Ann Arhor. Manuscript re<:eived April HJ; revision aceeptt·d Jmu• 13. Reprint requests: Dr. f:sclu•nbaclwr; Pulmcmar!J l'rmcticm l~1h, Unitlt'rsit!l of Michigan Mc•dical Center; Ann Arbor .J/J/()9-0026

straightforward technique for arriving at an interpretation of these tests has resulted in a more consistent approach to interpretation and an excellent teaching guide for physicians and technicians. (Chest 1990; 97:263-67)

MV\' =maximal voluntary ventilation; AT= anaerobic threshold; VR=ventilatory reserve; HRR=heart rate response;

HR, and Sa02 • With this algorithm, we can evaluate a patient's response to exercise and determine whether there was limitation to exercise lwcause of the lungs, the heart, or both. MATERIALS AND 1\IETIIOI>S

Cardiopulmonary t•xerdst' h'sts wt•n· ordered hy pulmonary physicians in our division and pt•rlimned on patients with primary pulmonary dist'ases: chronic obstrnl'livt' pulmonary diSt'aSt': dilfust' intt'rstitial fibrosis: pulmonary vaseular diseast•; t'rlimm•d using a treadmill (Marquette Electronil's st•rit•s 182.5) and an ext•rl'ise system analyzer li>r the analysis of exhaled gases and t•xhaled wntilation (Medil'al Graphics system 2001). Tlw protoc.11l uSt•d IC>r thest• studit•s was t•ither tlw pulmonary pmtrmant·t• prot1 as outlim•d in tlw manual li>r tlw tn•admill (Marquetlt• Electronic.-s, hll'). In addition, t•lt•l'lnK.·ardiographil' monitoring (Eaton Medical Croup nuKit•l C-2700) and noninvasive oximetry (llt•wlett-Pat·kanlnuKiei47201A) wen• pt•rlin·nwd on t•ach palit•nt during the ext•rl'ise protcK·ol. During tlw test. hlocKI pn•ssurt· was also nwasurt'd nsin~ a portabl .. sphygmomanomt'lt·r. Tlw Vt:, rPspiratory rate. tidal volunw, \·o,, and \'co, wt•n· mt•asurt'd on a breath-by-breath basis. Tt•stin~ was terminatt'd wht•n tht• patient si~nallt·d exhaustion, fatigut•, shortness of breath. It•!( pain. or du•st pain or wht•n STSt'!(ment ehanges or a eardiae arrhythmia was noted on tlw 12-lead ECC. The fi>llowing paramell'rs wt•re determined li>r t•aeh test and nSt•d fi>r tlw interpretation of tlw n•sults: \·o,; \·co,; \•t:: VR (VH =I - [\'Elnax/prl'dicted l\1\\']): n·ntilatory er t•ach t•xt•rcist• CHEST I 97 I 2 I FEBRUARY. 1990

263

I. PULMONARY LIMITAnON TO EXERCISE

HGFEDCBA

J

II. CARDIAC LIMITAnON TO EXERCISE

Q

R

KL

0

P

>50

S

T

uv

test.' The algorithm that we used for the actual interpretation of the results of cardiopulmonary exercise tests is shown in Figure 1. In this approach, there were certain parameters that were used as decision points for the evaluation of pulmonary and cardiac or circulatory limitation to exercise. The first parameter that was examined was the Vo2 max. This value for the patient should have been more than 90 pen:ent of the predicted maximal value for that patient. The predicted values for vo.max were determined by regression equations and used by Medical Graphics Corp in their equipment.' When using separate equations for underweight and normal individuals vs obese individuals, Wasserman et al<.a have shown that subjects without pulmonary or cardiac limitation to exercise should achieve approximately 100± 10 percent of the predicted Vo2 max. Therefore, we have arbitrarily set 90 percent of predicted Vo2 max as the lower limit of normal. We realize that a more statistically appropriate guide could be used (eg, 95 percent confidence interval); however, we have found this limit of90 percent to be simple to use and easy to teach. If an individual is able to achieve 90 percent or greater of his or her predicted vo.max, they may still have some pulmonary or cardiac limitation, but obviously, it would be mild in quality to allow them to achieve close to their predicted Vo2rnax. On the other hand, if the patient is not able to achieve 90 percent of his or her predicted vo.max, then the pulmonary or cardiac limitation, if present, would be either moderate or severe in quality. The next decision parameter that we used was the VR: VR=[l- (VEmaxlpred MVV)]

X

100%

where the VEmax is the maximal minute ventilation achieved with exercise, and the predicted MVV is determined by 41 X FEV,.• When an individual without pulmonary limitation exercises to a

284

MN

w

FIGURE 1. Algorithm for interpretation of cardiopulmonary exercise tests. VE, Ventilatory equivalent for carbon dioxide; S, change in Sa02 ; IS, ischemic symptoms (chest pain, s:r-segment changes, etc); and AT%, ratio of AT to Vo2max. For explanation of interpretations, A through W, see Table 1.

Vo.max; he or she will still exhibit some VR. One report suggests that without pulmonary limitation, this reserve should be greater than 30 percent.• Patients with pulmonary disease may have no ventilatory reserve left at their vo.max. Patients with less than 30 percent VR are said to have a ventilatory mechanical limitation. The next parameter that we used in our algorithm is the VEmaxl Vco2 • This value is a good overall determinant of the efficiency of the lung as a gas exchange unit. Normally, at maximal exercise, this value will be 25 to 35,' and values above 40 represent an excessive ventilation that is necessary to overcome the inability of the lung to excrete carbon dioxide due to gas exchange problems. Patients with values of VEmaxlVco2 of greater than 40 are said to have a gas exchange abnormality; however, another possibility for an increased ventilatory equivalent is any abnormal drive to ventilation such as anxiety. Usually, anxiety at the beginning of an exercise study can result in a ventilatory equivalent that is greater than 40; however, as exercise proceeds, this value will decrease as the drive to ventilation becomes more dependent upon the factors associated with exercise metabolism. This value will also increase again towards maximal exercise. The cutoff value that was chosen (40) should take into account the normal increases in this value with maximal exercise.' Finally, for the determination of pulmonary limitation to exercise, we examined the change in Sa02 either by arterial blood gas determinations or by noninvasive oximetry. The acccuracy of oximeters in measuring a change in oxygen saturation is ± 2.5 to ± 3.5 percent (95 percent confidence limits). 7 Therefore, a decrease in oxygen saturation of more than 4 percent is considered to be abnormal. In the context of exercise testing, desaturation can occur most <.'Ommonly in patients with diffusion limitations,• although other pulmonary abnormalities, such as shunts or ventilationperfusion mismatching, may result in exercise-associated desaturaInterpretation ol Cardiopulmonary Exercise Tests

(Eschenbac~

Mtullllna)

Table 1-Interpretative Results Using Algorithm

250

ABNORMAL HEART RATE RESPONSE

~

200

150

100

50

0

1000

2000

3000

4000

5000

6000

Vo2,mllmln Frct rnE 2. Normal and ahnormal responst·s fo.r increase in IIR during exercist• when plottt•d against increasing Vo,max. lion . Therel<1re, palit•nls with desatnration with exerdse an• said to have a dilfnsion·lype limitation. Afte r estahlishing whether the patie nt either dot•s or does not han• a pulmonary limitation to t•xt•rcise , wt• tht•n determined whether a t•ardiac or circulatory limitation to exe rcise may t•xist. Onr first dt'cision paranlt'lt·r li1r this determination was the IIRR. Normally. tlwre should he a linear relationship l)t'tween oxygen consumption and IIR .'' If tllt'rt' art· problems with tlw heart as a pump (eg, a cardiomyopathy), the IIRH at any oxygen consumption may he inappropriately increased. As shown in Figure 2. the normal increases in II H with t•xercist• are shown in tlw lowt•r shad .. d area. An ahnormal increase in II H with t•xercist• is shown in tlw shadt•d area ahow tht· normal area. \\{> can caknlalt• IIRH hy the li1llowing limnnla: IIRR = (IIHmax -IIHresl)~

' o , max-

Vo,resl)

where IIHmax is tlw heart rate at m;tximal t•xercise, HHresl is tht• heart ralt• at rest. Vo,max is till' maximal oxyge n l1>11S11mption in liters Jlt'r minnie. and \•o,resl is the oxygt•n l1lllsnmplion at rest in liters per minnie. Normally, this ratio (IIHH) will he 25 to 3.5 lin· trained indh·idnals and 3.5to 451i•r sedentary or untrained subjects. Patients with a cardiomyopathy or det1mditioning nr otlwr "cardiac pump" prohlem may have a IIRH of more than 50. This value of 50 as a cntolf point hetween normal individuals and individuals with ht'arl dist•ase or det'lnditioning was chosen arbitrarily hnt was based upon the reported data li•r normal individuals.'' Tht'St' valtlt's appl)· only to patients who are nul taking a medication that t1mld hlnt:k the IIRR In t'xercist·. Fc•r example , if a patient is receiving ~-adrenergic blockade. his nr llt'r HHH In ext•rcise can he dt•· creased;"' hm\·en•r, using this paramt'lt•r. we can also identil~ · patients who did nul give a maximal dli•rl and had a rednt·l'd \ 1o,max. Their IIHH will still he normal. Also, patit•nts who did not achieve tlwir Vo,max because nf only Vt'ntilatory limitation shnnld also have a normal HHH; howt•\'t'r, thnst' patients with hoth a ventilatory and cardiac nr circulatory limitation can he identifit'd hy having an increased IIHH and a pulmonary limitation In exerdse identified hy the parameters listed previnnsl): If the H RR is normal (<50), ,,.,. the n dl'lermined if the t'Xercist• lest was stopped hecanst• of electrot:ardiographic changes (depressed ST segments, arrhythmias, l'lc) or l)t'('anse of dwsl pain nr hypotension. These all can suggest an ischemic cardiac limitation to exercise (IS= ischemit· symptoms). Finally, we examined tlw AT. We delt•rmined the ratio of the oxygen consumption at the AT with the actual Vo,nuLx achieved or the predicted Vo,rmLx. If this ratio is less than 40 percent, this suggests a circulatory nr "pump" limitation to t•xerdse. Normally. this ratio is 55 to 60 percent.' It can l>t' decreased because the exercising mnsdes have switched over to anaerobic nwtahnlism at

I. Pulmonary limitation In exercise A. No pulmonary limitation or dt•crt'ast'd t•lli•rl or cardiac limitation B. Mild dilfusion·lype limitation C. Mild gas exchange ahnorrnality D. Mild gas exchange almormality and dilfnsion·lypt· limitation E. Mild ventilatory mechanical limitation F. Mild ventilatory mt·chanieal limitation and dilfnsinn·type limitation C . Mild ventilatory mechanical limitation and ~as exchange abnorrnality II. Mild ventilatory mt•chanieal limitation and gas exd1ange abnormality and dilfnsiorHype limitation I. Decrt•ased t•lli•rl nr cardiac limitation J. McKie rale or St'Vert• dillirsiorHypt• limitation K. McKit·raiP or severt• gas exdlangP ahnorrnality L. McKlt•rah' or St'H'rt' gas t•whange abnorrnality and dillilsion· type limitation !\1. l\lcKierate or spven· n•ntilatory nwehanieallirnitatiun N. McKierale or St'\'t'rt' n •ntilatory mt'l·hanical limitation and dilfnsiorHypt• limitaticm 0. McKit•ralt• or st•n•rt• n •ntilatnry rnt•chanicallirnilation and gas t•xdlange ahnorrnality P. MtKierale or seven• ventilatory mt•chanieallimilalion and gas t'xchangt• almorrnality and dill'nsiorHypt• limitation II. Cardiac or circulatory limitation to exerdSt· Q. McKieralt• or st•n•n• cardiac "pump" limitation (cardiomyopa· thy ; deconditioning) R. Cardiac "pnrnp" limitation (eanliomyopathy: det,mditioning) S. Cardiac "pump" limitation and circulatory limitation (pulmo· nary vaseular or peripheral vaseular tliSt•ase. or " pump" limitation) T. l\lcKieralt· or S<·ven· pulmonary limitation (S<'t' J through I') or IJC~•r elli•rl L1 . 1\o oll\·ious eardiac or cireulatory limitation V. Circulatory limitation (pulmonary \·ast·ular or periplu·ral ,·as· eular dist'aSt', or "pump" limitation) \\' Isdlt'mic heart diseast•

Table 2-Use of Algorithm for 52-Year-Old Woman u·ith S11spected P11lrrwnary Vasc11lar Di•ease* Data

lkst

\ ·o,. mVmin \'co,, rnVmin VE . IJmin

2SO 240 H.6 411.:3 H.5 9.'3

\ · E~ ' co,

SaO, % IIR , hprn AT, mVmin

Maximal EXt•rl'iS<•

I. OSI 1.2.5H 62.H .')().2 SH 15.'3 421;

*Baseline pulmonary function lt•sts: FEV,. 2.61; lis (1021lt.'rcenl of prediclt'd); FVC, 3.R6 L (Ill pt'rt't'nl of prt•dieted); and Dt", 12.24 rnVrnin/rnm llg (46 pe rcent of pn•dided). Caleulations: Vo,maxl Vo,nutx predielt'd =I ,OS I/I ,457 = 74 pt•rePnt: VH = 1- (\'nnaxlpn·diclt'd MVV)={I-(62.H/(2.61lx4l)l}x 100 = 41.3 J)l'rct'nl; IIHH= (IIHmax -IIHt•st)No,rnax- Vo, rest) = (15:3- H3)/(I.Oill- .2SO) = or (\'o,ATA'o,mt'rcenl = (421;/l,llll) X 100 or (42S/1.457) X J()() = :3!).6 or 2H.4 pt•reenl. l ' sing algorithm: Land S: mcKit•ratt• or St'\'t'rt' gas exchangt• and dilfusion·tnw pulmonary limitation and eardiac " pnmp" and l'irculatory limitation ("•mpatihle with pulmonary vascular diS<•aS<·). CHEST I 97 I 2 I FEBRUARY. 1990

265

an earlier workload because of the inability of the heart or the cin:ulation to provide the net:essary oxygen for aerobic metabolism. If the AT is not reached at all, this suggests that there is either a pure moderate to severe pulmonary limitation to exercise, a mixed pulmonary and cardiac limitation, or poor effi1rt by the patient. Using the algorithm shown in Figure 1, we were able to arrive at the different interpretative diagnoses that are listed in Table 1. Each letter, A through W, represents the end of a pathway in the algorithm. RESULTS

Using this algorithm, we have interpreted more than 20 cardiopulmonary exercise tests that were performed in our laboratory. We have found that the interpretation of the tests when using this algorithm not only gave a more consistent result but also was an improvement upon the interpretation by our pulmoTable 3-Compariaon of Use of Our Algorithm with Algorithm ofWoasennan et fill* Case

Our Interpretation

1 2

Normal or decreased effort Normal or decreased effort

3

Decreased effort

4

Mild ventilatory mechanical limitation Moderate or severe ventilatory mechanical limitation Moderate or severe ventilatory mechanical limitation and gas exchange abnormality and diffusion-type limitation Cardiac "pump" limitation (cardiomyopathy; demnditioning) Cardiac ''pump" limitation (canliomyopathy; deconditioning) Cardiac "pump" limitation (canliomyopathy; demnditioning) Moderate or severe gas exchange abnormality with cardiac "pump" limitation and circulatory limitation (pulmonary vascular or peripheral vascular disease or "pump" limitation) Moderate or severe gas exchange abnormality and diffusion-type limitation with cardiac "pump" limitation and circulatory limitation (pulmonary vascular or peripheral vascular disease, or "pump" limitation)

5

6

7

8

9

10

11

Interpretation of Wasserman et al• Normal Obesity usually with low breathing reserve Obesity usually with low breathing reserve Obesity usually with low breathing reserve Obstructive pulmonary disease Obstructive pulmonary disease

Early cardiovascular disease Obesity usually with low breathing reserve Poor effort or musculoskeletal disonler Pulmonary vascular disease without rightto-left shunt

Early pulmonary disease; pulmonary vascular disease

nary faculty in several instances. An example of the use of the algorithm is shown by interpreting the results of an exercise test for a patient with suspected pulmonary vascular disease (Table 2). In this example, the woman with possible pulmonary vascular disease has normal pulmonary mechanics as part of her baseline pulmonary function tests but a decrease in her value for Dco. By exercise testing, we determine that she was not able to achieve her predicted Vo2 max, but she had a normal VR; however, the patient had an increased VEmaxlVco2 , and she had desaturation with exercise. In addition, she had an abnormal HRR (74.9), and her AT was less than 40 percent of either her Vo 2 max or her predicted Vo2max. These factors taken together suggest that she has both pulmonary and cardiac limitation to exercise. We have compared our algorithm with the algorithm provided by Wasserman and others. 2 We have taken 11 representative studies from our laboratory and used our algorithm and the algorithm of Wasserman and associates2 to obtain interpretations of these tests. The results of this comparison is shown in Table 3 (the example shown in Table 2 is patient 11). We were pleased to find that for nine of the 11 examples, the two algorithms gave quite similar interpretations, especially in suggesting the same organ system that could be limiting. In the two exceptions (patients 8 and 9), we had suggested that some deconditioning or cardiac "pump" limitation could have existed, whereas by the algorithm of Wasserman et al2 the limitation could have been due to obesity, poor effort, or musculoskeletal disorder. It is possible that both algorithms may be right in these two patients, in that these diagnoses are not mutually exclusive. DISCUSSION

We have described the use of an algorithm that will simplify the interpretation of a cardiopulmonary exercise test. As its decision points, this algorithm uses parameters that are routinely obtained during the performance of an exercise test that includes the measurement of exhaled gases. This method allows for the interpretation of a cardiopulmonary exercise test in a straight-forward manner, so that an objective assessment of limitation to exercise can be determined. Using this method, we can also differentiate between a pulmonary and a cardiac or circulatory limitation to exercise. Previously, other than the algorithm from Wasserman and colleagues, 2 only general guidelines were available for the interpretation of these exercise tests. 11 - 13 Use of this algorithm can result in a specific interpretation for the patient based upon objective test results. We believe that this approach will be quite useful for the evaluation of patients with known pulmonary or cardiac disease (or both) or for the patient with unexplained dyspnea, especially when Interpretation ol cardiopulmonary Exen:ise Tests (Eschenbache(

Mannina)

the results are combined with routinely obtained pulmonary function studies. From a teaching perspective, this algorithm has resulted in a greater understanding and more consistent interpretations of cardiopulmonary exercise tests by our medical residents, pulmonary fellows, and pulmonary faculty. REFERENCES

7

8

9

1 Ellestad MH. Stress testing: principles and practices. Philadelphia: FA Davis, 1986:22,136 2 Wasserman K, Hansen JE, Sue DY, Whipp BJ. Principles of exercise testing and interpretation. Philadelphia: Lea and Febiger, 1987 3 Wasserman K, Whipp BJ. Exercise physiology in health and disease. Am Rev Respir Dis 1975; 112:219-49 4 Hansen JE, Sue DY, Wasserman K. Predicted values for clinical exercise testing. Am &v Hespir Dis 1984; 129:S49-55 5 Miller WF, Scacci R, Gast LR. Laboratory evaluation of pulmonary function. Philadelphia: JB Lippincott Co, 1987:300 6 Nery LE, Wasserman K, French W. Oren A, Davis JA. Contrasting cardiovascular and respiratory responses to exercise in mitral

10

11 12

valve and chronic obstructive pulmonary diseases. Chest 1983; 83:446-53 Ries AL, Farrow JT, Clausen JL. Accuracy of two ear oximeters at rest and during exercise in pulmonary patients. Am &v Respir Dis 1985; 132:685-89 Owens GR, Bogers RM, Pennock BE, Levin D. The diffusing arterial oxygen desaturation during capacity as a predictor exercise in patients with chronic obstructive pulmonary disease. N Eng) J Med 1984; 310:1218-21 Legge BJ, Banister EW. The Astrand-Ryhming nomogram revisited. J Appl Physiol1986; 61:1203-09 Joyner MJ, Freund BJ, Jilka SM, Hetrick GA, Martinez E, Ewy GA, et al. Effects of beta-blockade on exercise capacity of trained and untrained men: a hemodynamic comparison. J Appl Physiol1986; 60:1429-34 Wait J. Cardiopulmonary stress testing: a review of noninvasive approaches. Chest 1986; 90:504-10 Weber KT, Janicki JS, McElroy PA, Reddy HK. Concepts and applications of cardiopulmonary exercise testing. Chest 1988;

or

93:843-47 13 Neuberg GW, Friedman SH, \\\!iss MB, Herman MV. Cardiopulmonary exercise testing: the clinical value of gas exchange data. Arch Intern Med 1988; 148:2221-26

Plan to Attend ACCfPs

56th Annual Scientific Assembly Toronto, Ontario, canada

October 22-26, 1990

CHEST I 97 I 2 I FEBRUARY, 1990

267